Variable valve drives are utilized in vehicles with internal combustion engines to control the timing of engine cylinder valves in order to raise engine performance, increase fuel economy, and reduce emissions. Variable valve drives can be hydraulically controlled, an electronic controller of a powertrain control module directing high pressure oil to actuate oil pressure cams for altering valve timing.
The inventors herein have recognized various issues with the above system. For example, fully variable valve drives are expensive. Known partially variable valve drives may not provide individual control of the valves in order to optimize engine efficiency and the combustion process, and/or may not provide sufficient oil pressure to generate sufficient torque at different operating conditions.
One approach that at least partially addresses the above issues is a partially variable valve drive system comprising at least one cylinder head with at least one cylinder, each cylinder having at least two inlet openings for the supply of fresh air via an intake system and/or at least two outlet openings for the discharge of the exhaust gases via an exhaust-gas discharge system, a pump for delivering engine oil, the pump serving for supplying engine oil to the internal combustion engine, thus forming an oil circuit, and at least two at least partially variable valve drives having at least two valves which are movable between a valve closed position and a valve open position in order to open up and block the at least two inlet or outlet openings of a cylinder, having valve spring means for preloading the valves in the direction of the valve closed position, and having at least two hydraulically adjustable actuating devices for opening the valves counter to the preload force of the valve spring means, each actuating device comprising a cam which is arranged on a camshaft and which, as the camshaft rotates, can be brought into engagement with at least one cam follower element, whereby the associated valve can be actuated, wherein each hydraulically adjustable actuating device can be charged with pressurized oil via an oil pressure line which branches off from the oil circuit, there being arranged in the oil pressure line a controllable shut-off element which blocks or opens up the oil pressure line), and the cams of the at least two hydraulically adjustable actuating devices of the at least two at least partially variable valve drives are rotatable.
In this way, it may be possible to achieve a fully flexible valve train wherein individual control and actuation of each valve may be achieved via separate oil pressure lines. Further, this system provides a modular oil pressure actuated variable valve actuation which may be combined with a cam-in-cam system or a camshaft profile switching system, providing optimized, individual, variable valve lift and/or timing and a support system for providing sufficient oil pressure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.